I. Field of the Invention
The present invention relates generally to earthen formations and to related structures for soil reinforced retaining walls. More particularly, the present invention relates to geogrids and walls reinforced with geogrids of the type classified in United States Patent Class 405, Subclasses 258, 262, and 284.
II. Description of the Prior Art
Plastic reinforcement grid systems are used extensively in the construction of soil reinforced, segmental block retaining walls and reinforced slopes. So-called geogrids are available in a variety of sizes and configurations. The generally planar, sheet-like material typically comprises bidirectional, reinforcement grids. Typically the web-like material is installed adjacent layered block walls, with portions of the geogrid captivated by abutting blocks. Tensile strength is exhibited in both primary and secondary directions. Geogrid use has increased significantly over the last twenty years. Various building codes, regulations, and design standards now mandate the inclusion of reinforcing grids when retaining walls are built, or when slopes are reinforced. Geogrid use will likely increase in the future.
Geogrids are typically manufactured from high tenacity, plastic or polyester yarns. The grids may be woven, knitted, drawn, or extruded and then coated with a protective material. The coating material typically comprises high density polyethylene or polyvinyl chloride. Geogrids form an interlocking pattern with a plurality of regularly spaced apart voids. The grids are distributed upon and dispensed from large rolls. Preferred geogrid structures are stable, and resist creeping and deformation. Proper design and use minimizes installation damage, overstress, and elongation. In addition, the grid structure must resist chemical and biological degradation. Typical grids must be pliable for installation. They should be resistant to temperature and moisture extremes, soil chemicals and ultraviolet exposure. The so-called "Long Term Design Strength" for by modern geogrids provides a safe and efficient means of erecting safe and stable, soil-reinforced structures.
U.S. Pat. Nos. 5,267,816, 5,632,571 and 5,096,335 show plastic geogrids used for construction reinforcement.
U.S. Pat. No. 5,540,525 shows a modular block retaining wall system that may employ reinforcing geogrids. The modular blocks stack together to form a wall, and interconnect with portions of the geogrid reinforcing web.
U.S. Pat. No. 4,856,939 depicts a system employing wire trays to strengthen a geogrid reinforcement.
U.S. Pat. Nos. 4,767,237, 4,449,098, 4,597,183, and 4,852,263 show various systems for measuring the length of linear elements.
Once a geogrid structure is buried in the ground behind a segmental block wall or in a reinforced slope, the installed length is very difficult to determine through conventional means. Obviously, once the geogrid is buried in the ground, only small edge portions are visible to the human eye. Geogrid length is one of the most significant design parameters related to the strength of segmental block walls and reinforced slopes. In walls, the length of the geogrid is directly related to critical factors such as wall sliding, overturning, bearing capacity and global stability. The length of the geogrid in reinforced earth structures is related to the steepness and stability of the slope.
On infrequent occasions when reinforced segmental block retaining walls or reinforced slopes fail, it is imperative that geogrid length be ascertained to assess the stability of the remainder of the wall or slope. In addition, verification of geogrid lengths after construction and before final acceptance by the owner or Architect/Engineer is useful to verify that the wall or slope has been constructed in accordance with the specified design. At the present time, most reinforced slopes and retaining walls are constructed without adequate inspection by the owner, or the Architect/Engineer.
Thus an efficient means of geogrid length determination in conjunction with reinforced slopes and segmental block walls would be a useful and cost effective method of design verification after construction. Such a system would be an invaluable tool for forensic investigation. Moreover, an efficient system for geogrid length measurement would make it easier to verify contractor compliance with soil-reinforced structure specifications.